Imp v0.9.0

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Imp is a framework for typed, optimizable language-model programs on the BEAM. This release stops a native-tool ReActV2 step with one text output from asking the model to finish two contradictory ways. The prompt the model receives changes, so this is a minor release rather than a patch.

Install

{:imp, "~> 0.9"}

Every dependency comes from Hex. Use a path dependency only while developing against a local checkout.

ExMCP and erlexec are declared runtime: false, so an OTP release that uses Imp.ACP or Imp.MCP must list applications: [ex_mcp: :load, erlexec: :load] in its release definition; see releases that use MCP or ACP. Ordinary Imp startup starts no protocol endpoint.

Changes and upgrading from 0.8

  • For an LM that calls tools natively and a task with one unconstrained text output (no submit tool), ReActV2's system message no longer asks for [[ ## answer ## ]] and [[ ## completed ## ]] markers while also saying the answer is the message sent without a tool call. It lays out the inputs alone, with no history placeholder, and the loop line reads "When the final answer is ready, reply without calling a tool: that message is answer." Step demos and stored turns are shown as plain text. The input template comes from the signature, so the system message stays the same across steps and keeps the provider prompt-cache prefix.
  • Replies that still use markers parse as before. Written tool calls (an LM without native tool calling), signatures with submit, and the JSON and XML formats are unchanged. No data migration is needed: stored turns and saved demonstrations are rendered in the new form when replayed.

Change the Imp dependency to {:imp, "~> 0.9"}, run mix deps.update imp, and commit mix.lock. Migration: a test, fixture or custom renderer that matched the old system message text, or the marker-framed step demos, must match the new text. Rollback means restoring the previous dependency requirement, lock and application release; it restores the contradictory prompt too. Provider-free tests assert the exact system message and that marker replies still parse; this release does not establish how any particular model responds to the revised prompt. See the changelog for older changes.

Known limits

  • Imp.Usage does not see streamed calls: they run in a separate process, so usage tracked around Imp.collect or a streamed Imp.call is empty. Read usage from the run's :model_response events.
  • The usage map (:usage on the :model_response event, Imp.Usage, Imp.Prediction.get_lm_usage/1) is ReqLLM's, unchanged. For a non-streamed call its :cost and :total_cost are ReqLLM's catalog estimate, not a charge, and OpenRouter's charge is its "cost". Read money from cost and estimated_cost.
  • An error the provider sends inside a stream has status nil and retryable: true, because ReqLLM's stream decoder keeps only its message; the same error in a non-streamed response may carry a status that says not to retry.
  • A flat two-element name-first list that is not itself an element of a list (at the top level, in a tuple, or under a key that is not a credential name), such as ["password", "hunter2"], is not redacted, where 0.5.0 redacted it. Such a list is read as a key and value only as an element of a list, so that lists of names such as with_inputs([:api_key, :question]) survive saving.
  • The GEPA, SIMBA, MIPROv2, InferRules and random-search checkpoints redact their failure reasons but otherwise hold the resume state as it is: GEPA's candidates, evaluation cache, proposed instructions and reflection data, and the others' instructions, demos and scores. Fast-Slow and Playbook checkpoints likewise hold their prompts, rollouts and playbooks. Treat checkpoint files as sensitive.
  • A ReActV2 step whose prose quotes its own field names (a JSON object with next_thought or tool_calls keys, a [[ ## field ## ]] line, a <next_thought> tag) is not read as prose and goes to the JSON fallback, which usually costs one more call. If the model repeats the same reply, the step ends :incomplete. Beside native tool calls, such a thought becomes nil; the calls still run.
  • When a streamed ReqLLM request fails, ReqLLM's own warning log prints the error with its response headers. Imp strips them from the error it returns, but cannot change that log line.
  • In command output, a Bearer token of 12 to 15 characters, or one with no digit, is shown when more text or a newline follows it. 0.5.0's command pipeline hid any such token of 12 or more characters.
  • A GEPA checkpoint taken between preparing and starting a full validation resumes by rejecting that candidate, as before.

The CHANGELOG records every user-visible change in this release. Generated module documentation is the complete API reference. Start with Imp, Imp.Signature, Imp.Module, Imp.Evaluate, Imp.Optimizer, Imp.ACP, Imp.MCP, and Imp.Telemetry.