Agent Execution Models: Five Ways to Run

Claude Code supports five distinct agent execution models, each with different isolation levels, use cases, and cost profiles. All five share the forked agent pattern as their primitive, but they differ in where they run and how they're isolated.

The Five Models

Model	Isolation	Where it runs	Cache sharing	Use case
InProcessTeammate	AsyncLocalStorage (same process)	Same terminal	Full cache reuse	Lightweight parallel work
LocalAgentTask	Separate async process	Background	Cache prefix shared	Non-blocking sub-agents
RemoteAgentTask	Cloud container (CCR)	Anthropic cloud	No cache sharing	Full sandboxed execution
DreamTask	Background-only, memory writes only	Background	Cache prefix shared	Memory consolidation
Worktree Agent	Git worktree (own branch + directory)	Background or interactive	Cache prefix shared	Parallel code editing

The Shared Primitive: Forked Agents

All five models use the forked agent pattern from src/utils/forkedAgent.ts. The fork constructs a child agent using CacheSafeParams — byte-identical to the parent's API request prefix, enabling 92% prompt cache reuse. The child gets cloned mutable state (separate readFileState LRU cache, child AbortController, fresh denialTracking) but shares the cache prefix.

Anti-recursion: Fork children see the AgentTool in their pool but reject recursive fork attempts, checked via <fork_boilerplate_tag> marker.

Cost Model

The cache-sharing economics are dramatic: - Five parallel agents cost nearly the same as one (92% prefix reuse) - Measured savings: $4.85 (81% reduction) per representative task - Breaking cache alignment is catastrophic: PR #18143 tried effort: 'low' on a fork, cache dropped from 92.7% to 61%, writes spiked 45x

Only four parameters are safely overridable without breaking cache: abortController, skipTranscript, skipCacheWrite, canUseTool.

Worktree Isolation: Git as Virtualization

Instead of complex filesystem virtualization, Anthropic leveraged Git's built-in mechanism. Each worktree agent gets: - Isolated: own working directory, staging area, HEAD - Shared: .git/objects/ (history stored once), .git/refs/ (branches visible)

Five simultaneous worktree agents produce five independent branches merged through standard PR process. Cleanup is automatic on agent exit.

The COORDINATOR_MODE Vision

COORDINATOR_MODE (compiled out of standard builds) represents the most aggressive parallelism: one worker per logical CPU core. The coordinator's four-phase workflow: 1. Research — workers investigate codebase in parallel 2. Synthesis — coordinator alone reads findings and crafts specs 3. Implementation — workers make targeted changes per spec 4. Verification — workers run tests in parallel

Status: archived TypeScript, never ported to the current Bun+Rust stack.