Axle

Appearance

Upgrading ​

Every release has a full migration guide in the repository under docs/, one file each from 0.13.0-migration.md through 0.30.0-migration.md. This page is the map to them — what changed, and which ones you actually need to read.

Current release: 0.30.1.

0.30.0 — host-owned transcripts ​

This is the big one — the largest breaking change in the library's history. If you're on 0.29 or earlier, it's worth reading the full guide rather than just this summary.

Transcripts moved to the host. The agent no longer keeps renderable history.

typescript
// @check-skip — shows the pre-0.30 API
// before — agent owned it
agent.history;

// after — you own it
const transcript = new Transcript();
agent.on((event) => transcript.apply(event));
transcript.turns;

Use agent.messages for the active model-facing conversation. Persist transcript.turns alongside agent.snapshot() — the session no longer carries render state. See Transcripts.

TurnAccumulator → Transcript. Renamed, with the related persistence exports.

Built-in memory APIs removed. There's no automatic recall/record behaviour any more. Replace it with tools for model-directed memory, and Instruct.addContext() for host-provided context.

Session-level annotations removed. Annotations now attach to turns or parts instead. Session-wide application state is yours to keep.

Compaction restructured into three layers — triggers, shouldCompactOnTrigger, and compact — with stateful compaction parts and compaction:update / :complete / :error events. Automatic compaction failures are now recorded on the transcript without failing the user turn. See Compaction.

0.29.0 — step terminology ​

The tool-loop unit was renamed from "turn" to "step", because "turn" already meant the render-layer unit.

BeforeAfter
maxIterationsmaxSteps
"max-iterations""max-steps"
turn:start / turn:complete (stream events)step:start / step:complete
generateTurngenerateStep

If you're wondering why the rename happened: "turn" was already taken by the render layer, so the same word meant two different things. Glossary has the current vocabulary.

0.28.0 ​

  • Added agent.stop() and agent.clear().
  • Added PromptCompactor and automatic before/after-turn compaction triggers.

0.26.0 ​

  • Loop limits became stops, not errors. maxSteps and maxContextTokens return ok: true with stopped instead of an error result. Non-positive limits throw at call time. See Results & errors.
  • agent.history.log → agent.history.messages (and later agent.messages).
  • agent.snapshot() became async.
  • Agent.restore() removed — resume with new Agent(config, session).
  • index removed from StreamEvent; correlate tool events by id.
  • createHandle export removed.

0.25.0 ​

0.24.0 ​

  • Added experimental subagent tools and parallelize.
  • Agent.on() began returning an unsubscribe function.
  • Behavior change: in stream(), an onToolCall returning null/undefined falls through to the matching registry tool, matching generate().
  • Behavior change: a tool throwing an error merely named AbortError while the run's signal is live is reported as an ordinary tool error rather than aborting the run.

0.20.0 ​

  • The library and CLI split into separate packages. @fifthrevision/axle is the library; @fifthrevision/axle-cli is the axle command.
  • Added AgentSession, snapshot/restore, and createAgentConfig.

0.18.0 ​

  • Request options were standardized across providers — output tokens, temperature, top-p, stop sequences, tool choice, and provider-specific options. Provider option types and runtime parameters were renamed; see the guide.

0.17.0 ​

  • Instruct moved to object-style constructor options.
  • Instruct schema typing widened to any Zod schema.
  • Clearer errors for missing template variables. Full guide.

0.15.0 ​

0.13.0 ​

  • Provider tool registries, streamed tool output and arguments. Full guide.

About the CLI ​

@fifthrevision/axle-cli is being reworked, so it isn't documented on this site yet. You can still install it separately:

bash
npm install -g @fifthrevision/axle-cli

See also ​