rust-agent-sdk is an unofficial Rust port of Anthropic's claude-agent-sdk (Python). It does not talk to the Anthropic HTTP API — like the original, it spawns the claude CLI as a child process and speaks its stream-json control protocol over stdin/stdout, parsing the streamed events into typed Rust values on a tokio-native async surface.
The wire format becomes a Message enum with ten variants built from typed ContentBlocks; the options struct mirrors the Python SDK's roughly fifty fields — model, tools, permission modes, MCP servers, hooks, budgets, a can_use_tool callback. Two entry points, same as upstream: one-shot query(), or a persistent bidirectional ClaudeSDKClient you can interrupt, reconfigure and drive mid-session.
Sessions as a first-class concern
The part I care most about is session management, because it's the part agent harnesses usually get wrong: list, fork, rename, tag and delete sessions; resume or continue; import external JSONL transcripts; fold an incremental summary as messages arrive.
Persistence goes through a SessionStore trait, and this is where the design earns its keep. Three implementations ship in the crate: in-memory, Postgres (sqlx) and Redis — the SQL one using unnest with ORDINALITY to keep message order stable, the Redis one indexing sessions in a ZSET. All three pass the same conformance suite, and the Postgres and Redis stores are additionally validated live against real Postgres 16 and Redis 7 in Docker. Both are feature-gated (postgres, redis-store), so nobody pays for a dependency they don't use. One contract, N implementations, one shared proof of correctness — that's the pattern.
Honest edges
793 tests total; about 56 of them require the claude binary on PATH, so ~737 pass without it — the README says exactly that. S3 is not implemented; it's on the roadmap, labeled as such. This is a port, not an original design, and I state that in the first line: the value is in porting a nontrivial contract faithfully — subpath sentinels, delete cascades, millisecond mtimes — and proving the port with tests rather than promises.