diff --git a/toolchain/driver/BUILD b/toolchain/driver/BUILD
index 911c1b4249f3..90ce5082466a 100644
--- a/toolchain/driver/BUILD
+++ b/toolchain/driver/BUILD
@@ -127,26 +127,64 @@ cc_library(
 )
 
 cc_library(
-    name = "compile_driver",
-    srcs = [
-        "compile_driver.cpp",
-        "compile_options.cpp",
+    name = "driver_env",
+    hdrs = ["driver_env.h"],
+    deps = [
+        ":runtimes_cache",
+        "//common:ostream",
+        "//toolchain/base:install_paths",
+        "//toolchain/diagnostics:emitter",
+        "@llvm-project//llvm:Support",
     ],
-    hdrs = [
-        "compile_driver.h",
-        "compile_options.h",
-        "driver_env.h",
+)
+
+cc_library(
+    name = "driver_subcommand",
+    srcs = ["driver_subcommand.cpp"],
+    hdrs = ["driver_subcommand.h"],
+    deps = [
+        ":driver_env",
+        "//common:command_line",
+        "//common:ostream",
+        "//toolchain/base:install_paths",
+        "@llvm-project//llvm:Support",
     ],
+)
+
+cc_library(
+    name = "compile_options",
+    srcs = ["compile_options.cpp"],
+    hdrs = ["compile_options.h"],
     deps = [
         ":codegen_options",
-        ":runtimes_cache",
-        "//common:check",
+        ":driver_env",
         "//common:command_line",
         "//common:error",
         "//common:ostream",
+        "//toolchain/base:clang_invocation",
+        "//toolchain/check",
+        "//toolchain/diagnostics:emitter",
+        "//toolchain/lower:options",
+        "//toolchain/parse",
+        "@llvm-project//llvm:MC",
+        "@llvm-project//llvm:Passes",
+        "@llvm-project//llvm:Support",
+        "@llvm-project//llvm:TargetParser",
+    ],
+)
+
+cc_library(
+    name = "compile_driver",
+    srcs = ["compile_driver.cpp"],
+    hdrs = ["compile_driver.h"],
+    deps = [
+        ":codegen_options",
+        ":compile_options",
+        ":driver_env",
+        ":runtimes_cache",
+        "//common:error",
+        "//common:ostream",
         "//common:pretty_stack_trace_function",
-        "//common:raw_string_ostream",
-        "//common:version",
         "//common:vlog",
         "//toolchain/base:clang_invocation",
         "//toolchain/base:install_paths",
@@ -162,17 +200,224 @@ cc_library(
         "//toolchain/lower:options",
         "//toolchain/parse",
         "//toolchain/parse:tree",
-        "//toolchain/sem_ir:file",
         "//toolchain/sem_ir:typed_insts",
         "//toolchain/source:source_buffer",
-        "@llvm-project//clang:codegen",
-        "@llvm-project//clang:frontend",
-        "@llvm-project//clang:lex",
         "@llvm-project//llvm:Core",
         "@llvm-project//llvm:MC",
         "@llvm-project//llvm:Passes",
         "@llvm-project//llvm:Support",
         "@llvm-project//llvm:Target",
+    ],
+)
+
+cc_library(
+    name = "compile_subcommand",
+    srcs = ["compile_subcommand.cpp"],
+    hdrs = ["compile_subcommand.h"],
+    deps = [
+        ":compile_driver",
+        ":compile_options",
+        ":driver_env",
+        ":driver_subcommand",
+        "//common:command_line",
+        "//toolchain/diagnostics:emitter",
+        "//toolchain/diagnostics:format_providers",
+        "@llvm-project//llvm:Support",
+    ],
+)
+
+cc_library(
+    name = "format_subcommand",
+    srcs = ["format_subcommand.cpp"],
+    hdrs = ["format_subcommand.h"],
+    deps = [
+        ":driver_env",
+        ":driver_subcommand",
+        "//common:command_line",
+        "//common:error",
+        "//common:ostream",
+        "//common:raw_string_ostream",
+        "//toolchain/base:install_paths",
+        "//toolchain/base:shared_value_stores",
+        "//toolchain/diagnostics:emitter",
+        "//toolchain/format",
+        "//toolchain/lex",
+        "//toolchain/source:source_buffer",
+        "@llvm-project//llvm:Support",
+    ],
+)
+
+cc_library(
+    name = "language_server_subcommand",
+    srcs = ["language_server_subcommand.cpp"],
+    hdrs = ["language_server_subcommand.h"],
+    deps = [
+        ":codegen_options",
+        ":driver_env",
+        ":driver_subcommand",
+        "//common:command_line",
+        "//toolchain/diagnostics:emitter",
+        "//toolchain/language_server",
+        "@llvm-project//llvm:Support",
+    ],
+)
+
+cc_library(
+    name = "carbon_runtimes",
+    srcs = ["carbon_runtimes.cpp"],
+    hdrs = ["carbon_runtimes.h"],
+    deps = [
+        ":codegen_options",
+        ":compile_driver",
+        ":compile_options",
+        ":driver_env",
+        ":runtimes_cache",
+        "//common:check",
+        "//common:error",
+        "//common:ostream",
+        "//common:string_helpers",
+        "//common:vlog",
+        "//toolchain/base:install_paths",
+        "//toolchain/base:runtimes_build_info",
+        "@llvm-project//llvm:Support",
+        "@llvm-project//llvm:TargetParser",
+    ],
+)
+
+cc_library(
+    name = "link_subcommand",
+    srcs = [
+        "link_driver.cpp",
+        "link_options.cpp",
+        "link_subcommand.cpp",
+    ],
+    hdrs = [
+        "link_driver.h",
+        "link_options.h",
+        "link_subcommand.h",
+    ],
+    deps = [
+        ":carbon_runtimes",
+        ":clang_runner",
+        ":codegen_options",
+        ":driver_env",
+        ":driver_subcommand",
+        "//common:check",
+        "//common:command_line",
+        "//common:error",
+        "//common:filesystem",
+        "//common:ostream",
+        "//common:vlog",
+        "//toolchain/base:install_paths",
+        "//toolchain/base:runtimes_build_info",
+        "@llvm-project//llvm:Support",
+        "@llvm-project//llvm:TargetParser",
+    ],
+)
+
+cc_library(
+    name = "build_subcommand",
+    srcs = ["build_subcommand.cpp"],
+    hdrs = ["build_subcommand.h"],
+    deps = [
+        ":codegen_options",
+        ":compile_driver",
+        ":compile_options",
+        ":driver_env",
+        ":driver_subcommand",
+        ":link_subcommand",
+        "//common:command_line",
+        "//common:error",
+        "//common:filesystem",
+        "//common:hashing",
+        "//common:ostream",
+        "@llvm-project//llvm:Support",
+    ],
+)
+
+cc_library(
+    name = "build_runtimes_subcommand",
+    srcs = ["build_runtimes_subcommand.cpp"],
+    hdrs = ["build_runtimes_subcommand.h"],
+    deps = [
+        ":carbon_runtimes",
+        ":clang_runner",
+        ":codegen_options",
+        ":driver_env",
+        ":driver_subcommand",
+        ":runtimes_cache",
+        "//common:command_line",
+        "//common:error",
+        "//toolchain/diagnostics:emitter",
+        "@llvm-project//llvm:Support",
+        "@llvm-project//llvm:TargetParser",
+    ],
+)
+
+cc_library(
+    name = "config_subcommand",
+    srcs = ["config_subcommand.cpp"],
+    hdrs = ["config_subcommand.h"],
+    deps = [
+        ":clang_runner",
+        ":codegen_options",
+        ":driver_env",
+        ":driver_subcommand",
+        "//common:check",
+        "//common:command_line",
+        "//common:filesystem",
+        "//common:ostream",
+        "//common:version",
+        "//toolchain/base:clang_invocation",
+        "//toolchain/base:install_paths",
+        "//toolchain/diagnostics:emitter",
+        "@llvm-project//clang:frontend",
+        "@llvm-project//clang:lex",
+        "@llvm-project//llvm:Support",
+        "@llvm-project//llvm:TargetParser",
+    ],
+)
+
+cc_library(
+    name = "clang_subcommand",
+    srcs = ["clang_subcommand.cpp"],
+    hdrs = ["clang_subcommand.h"],
+    deps = [
+        ":clang_runner",
+        ":driver_env",
+        ":driver_subcommand",
+        "//common:command_line",
+        "@llvm-project//llvm:Support",
+        "@llvm-project//llvm:TargetParser",
+    ],
+)
+
+cc_library(
+    name = "lld_subcommand",
+    srcs = ["lld_subcommand.cpp"],
+    hdrs = ["lld_subcommand.h"],
+    deps = [
+        ":driver_env",
+        ":driver_subcommand",
+        ":lld_runner",
+        "//common:command_line",
+        "@llvm-project//llvm:Support",
+        "@llvm-project//llvm:TargetParser",
+    ],
+)
+
+cc_library(
+    name = "llvm_subcommand",
+    srcs = ["llvm_subcommand.cpp"],
+    hdrs = ["llvm_subcommand.h"],
+    deps = [
+        ":driver_env",
+        ":driver_subcommand",
+        ":llvm_runner",
+        "//common:check",
+        "//common:command_line",
+        "//toolchain/base:llvm_tools",
+        "@llvm-project//llvm:Support",
         "@llvm-project//llvm:TargetParser",
     ],
 )
@@ -180,90 +425,36 @@ cc_library(
 cc_library(
     name = "driver",
     srcs = [
-        "build_runtimes_subcommand.cpp",
-        "build_runtimes_subcommand.h",
-        "build_subcommand.cpp",
-        "build_subcommand.h",
-        "carbon_runtimes.cpp",
-        "carbon_runtimes.h",
-        "clang_subcommand.cpp",
-        "clang_subcommand.h",
-        "compile_subcommand.cpp",
-        "compile_subcommand.h",
-        "config_subcommand.cpp",
-        "config_subcommand.h",
         "driver.cpp",
-        "driver_subcommand.cpp",
-        "format_subcommand.cpp",
-        "format_subcommand.h",
-        "language_server_subcommand.cpp",
-        "language_server_subcommand.h",
-        "link_driver.cpp",
-        "link_driver.h",
-        "link_options.cpp",
-        "link_options.h",
-        "link_subcommand.cpp",
-        "link_subcommand.h",
-        "lld_subcommand.cpp",
-        "lld_subcommand.h",
-        "llvm_subcommand.cpp",
-        "llvm_subcommand.h",
     ],
     hdrs = [
         "driver.h",
-        "driver_subcommand.h",
     ],
     data = [
         "//toolchain/install:all_data_files",
     ],
     textual_hdrs = ["flags.def"],
     deps = [
-        ":clang_runner",
-        ":codegen_options",
-        ":compile_driver",
-        ":lld_runner",
-        ":llvm_runner",
+        ":build_runtimes_subcommand",
+        ":build_subcommand",
+        ":clang_subcommand",
+        ":compile_subcommand",
+        ":config_subcommand",
+        ":driver_env",
+        ":driver_subcommand",
+        ":format_subcommand",
+        ":language_server_subcommand",
+        ":link_subcommand",
+        ":lld_subcommand",
+        ":llvm_subcommand",
         ":runtimes_cache",
         "//common:check",
         "//common:command_line",
         "//common:error",
-        "//common:filesystem",
-        "//common:hashing",
         "//common:ostream",
         "//common:pretty_stack_trace_function",
-        "//common:raw_string_ostream",
         "//common:version",
-        "//common:vlog",
-        "//toolchain/base:clang_invocation",
-        "//toolchain/base:install_paths",
-        "//toolchain/base:llvm_tools",
-        "//toolchain/base:runtimes_build_info",
-        "//toolchain/base:shared_value_stores",
-        "//toolchain/base:timings",
-        "//toolchain/check",
-        "//toolchain/codegen",
-        "//toolchain/diagnostics:emitter",
-        "//toolchain/diagnostics:format_providers",
-        "//toolchain/diagnostics:sorting_consumer",
-        "//toolchain/format",
-        "//toolchain/language_server",
-        "//toolchain/lex",
-        "//toolchain/lower",
-        "//toolchain/lower:options",
-        "//toolchain/parse",
-        "//toolchain/parse:tree",
-        "//toolchain/sem_ir:file",
-        "//toolchain/sem_ir:typed_insts",
-        "//toolchain/source:source_buffer",
-        "@llvm-project//clang:codegen",
-        "@llvm-project//clang:frontend",
-        "@llvm-project//clang:lex",
-        "@llvm-project//llvm:Core",
-        "@llvm-project//llvm:MC",
-        "@llvm-project//llvm:Passes",
         "@llvm-project//llvm:Support",
-        "@llvm-project//llvm:Target",
-        "@llvm-project//llvm:TargetParser",
     ],
 )
 
diff --git a/toolchain/driver/compile_driver.cpp b/toolchain/driver/compile_driver.cpp
index 881f3d334b4b..d87eac7eaf36 100644
--- a/toolchain/driver/compile_driver.cpp
+++ b/toolchain/driver/compile_driver.cpp
@@ -19,11 +19,14 @@
 #include "llvm/ADT/ScopeExit.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Module.h"
 #include "llvm/MC/TargetRegistry.h"
 #include "llvm/Passes/OptimizationLevel.h"
 #include "llvm/Passes/PassBuilder.h"
 #include "llvm/Passes/StandardInstrumentations.h"
 #include "llvm/Support/SaveAndRestore.h"
+#include "llvm/Target/TargetMachine.h"
 #include "toolchain/base/clang_invocation.h"
 #include "toolchain/base/timings.h"
 #include "toolchain/check/check.h"
@@ -62,6 +65,8 @@ CompilationUnit::CompilationUnit(
   }
 }
 
+CompilationUnit::~CompilationUnit() = default;
+
 auto CompilationUnit::IncludeInDumps() -> bool {
   return cache_->include_in_dumps().Get(check_ir_id_);
 }
@@ -421,6 +426,8 @@ auto CompilationUnit::LogCall(llvm::StringLiteral logging_label,
 
 CompileDriver::CompileDriver(CompileOptions* options) : options_(options) {}
 
+CompileDriver::~CompileDriver() = default;
+
 auto CompileDriver::Initialize(
     DriverEnv& driver_env,
     llvm::function_ref<auto(llvm::StringRef)->std::string> map_input) -> bool {
diff --git a/toolchain/driver/compile_driver.h b/toolchain/driver/compile_driver.h
index a63e16016d85..8da74ad20a0e 100644
--- a/toolchain/driver/compile_driver.h
+++ b/toolchain/driver/compile_driver.h
@@ -8,11 +8,16 @@
 #include <memory>
 
 #include "llvm/ADT/SmallVector.h"
-#include "llvm/Target/TargetMachine.h"
 #include "toolchain/diagnostics/sorting_consumer.h"
 #include "toolchain/driver/compile_options.h"
 #include "toolchain/driver/driver_env.h"
 
+namespace llvm {
+class LLVMContext;
+class Module;
+class TargetMachine;
+}  // namespace llvm
+
 namespace Carbon {
 
 class MultiUnitCache;
@@ -31,6 +36,7 @@ class CompilationUnit {
                            std::string output_filename,
                            const llvm::Target* target,
                            llvm::LLVMContext* llvm_context);
+  ~CompilationUnit();
 
   // Sets the multi-unit cache and initializes dependent member state.
   auto SetMultiUnitCache(MultiUnitCache* cache) -> void;
@@ -241,6 +247,7 @@ class MultiUnitCache {
 class CompileDriver {
  public:
   explicit CompileDriver(CompileOptions* options);
+  ~CompileDriver();
 
   // Configure the toolchain to compile all input files and dependencies.
   // The `map_input` function maps an input file name to an output file name.
diff --git a/toolchain/driver/compile_options.cpp b/toolchain/driver/compile_options.cpp
index fc57f6e510d7..ca4eef2a1a62 100644
--- a/toolchain/driver/compile_options.cpp
+++ b/toolchain/driver/compile_options.cpp
@@ -6,6 +6,8 @@
 
 #include <optional>
 
+#include "llvm/MC/TargetRegistry.h"
+#include "llvm/TargetParser/Triple.h"
 #include "toolchain/base/clang_invocation.h"
 
 namespace Carbon {
diff --git a/toolchain/driver/compile_options.h b/toolchain/driver/compile_options.h
index a85ce0520404..f8d30c328b77 100644
--- a/toolchain/driver/compile_options.h
+++ b/toolchain/driver/compile_options.h
@@ -10,15 +10,18 @@
 #include "common/ostream.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
-#include "llvm/MC/TargetRegistry.h"
 #include "llvm/Passes/OptimizationLevel.h"
 #include "toolchain/check/check.h"
 #include "toolchain/diagnostics/emitter.h"
 #include "toolchain/driver/codegen_options.h"
 #include "toolchain/driver/driver_env.h"
-#include "toolchain/lower/lower.h"
+#include "toolchain/lower/options.h"
 #include "toolchain/parse/parse.h"
 
+namespace llvm {
+class Target;
+}  // namespace llvm
+
 namespace Carbon {
 
 // Options for Carbon compilation. This struct is shared between the
diff --git a/toolchain/driver/driver_subcommand.cpp b/toolchain/driver/driver_subcommand.cpp
index 9678f470f018..1dc9f1ba5d4e 100644
--- a/toolchain/driver/driver_subcommand.cpp
+++ b/toolchain/driver/driver_subcommand.cpp
@@ -4,10 +4,6 @@
 
 #include "toolchain/driver/driver_subcommand.h"
 
-#include "llvm/TargetParser/Host.h"
-#include "llvm/TargetParser/Triple.h"
-#include "toolchain/driver/lld_runner.h"
-
 namespace Carbon {
 
 auto DriverSubcommand::TestAndDiagnoseIfFuzzingExternalLibraries(
diff --git a/toolchain/driver/runtimes_cache.cpp b/toolchain/driver/runtimes_cache.cpp
index 7e678bf9ff9b..adbfc93cca50 100644
--- a/toolchain/driver/runtimes_cache.cpp
+++ b/toolchain/driver/runtimes_cache.cpp
@@ -4,6 +4,8 @@
 
 #include "toolchain/driver/runtimes_cache.h"
 
+#include <unistd.h>
+
 #include <algorithm>
 #include <chrono>
 #include <filesystem>
diff --git a/toolchain/format/BUILD b/toolchain/format/BUILD
index 4b2e0cdfd269..5f4ca1631c07 100644
--- a/toolchain/format/BUILD
+++ b/toolchain/format/BUILD
@@ -21,8 +21,6 @@ cc_library(
     hdrs = ["format.h"],
     deps = [
         "//common:ostream",
-        "//toolchain/lex:token_index",
-        "//toolchain/lex:token_kind",
         "//toolchain/lex:tokenized_buffer",
     ],
 )
diff --git a/toolchain/language_server/BUILD b/toolchain/language_server/BUILD
index 454dfb5764bb..60579df93ade 100644
--- a/toolchain/language_server/BUILD
+++ b/toolchain/language_server/BUILD
@@ -61,6 +61,7 @@ cc_library(
         "//toolchain/diagnostics:file_diagnostics",
         "//toolchain/driver:codegen_options",
         "//toolchain/driver:compile_driver",
+        "//toolchain/driver:compile_options",
         "//toolchain/lex",
         "//toolchain/lex:tokenized_buffer",
         "//toolchain/parse",
diff --git a/toolchain/source/BUILD b/toolchain/source/BUILD
index 4e946ae1df71..8ad5b6f938cb 100644
--- a/toolchain/source/BUILD
+++ b/toolchain/source/BUILD
@@ -11,10 +11,8 @@ cc_library(
     srcs = ["source_buffer.cpp"],
     hdrs = ["source_buffer.h"],
     deps = [
-        "//common:error",
         "//toolchain/diagnostics:emitter",
         "//toolchain/diagnostics:file_diagnostics",
-        "//toolchain/diagnostics:format_providers",
         "@llvm-project//llvm:Support",
     ],
 )