Imp v0.16.0

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Imp is a framework for typed, optimizable language-model programs on the BEAM. This release adds request_retry: to Imp.Run.start/3, which sends a model request the provider failed in a way that may pass again in the same run, after a wait. It also changes two things a caller may rely on: an LM client other than ReqLLM reports its charge as metadata :cost, because Imp.Core no longer reads it from the usage map; and a ReActV2 forced submit with invalid arguments goes to the extractor. A new option and changed behaviour make this a minor release under Imp's versioning rule.

Install

{:imp, "~> 0.16.0"}

~> 0.16.0 takes later 0.16 patch releases and nothing newer. The two-part form, ~> 0.16, means >= 0.16.0 and < 1.0.0 in Mix, so mix deps.update imp under it takes every later 0.x release, including minor releases that change what callers receive.

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 0.15

Change the Imp dependency to {:imp, "~> 0.16.0"}, run mix deps.update imp, and commit mix.lock. No data migration is needed. Check the second item if you use an LM client of your own, or build response envelopes by hand.

  • Added: request_retry: on Imp.Run.start/3. request_retry: [waits: [ms, ...], reserve: ms] sends a model request that failed with an error Imp.Errors.retryable?/1 accepts (408, 425, 429, 5xx, a failed connection) again inside Imp.LM.request/2, after each wait in turn. Under a deadline the last wait repeats while it leaves reserve (60 s by default) of the deadline; without one, the list is the bound. A provider's retry-after longer than the wait is waited instead. Each attempt is its own :model_request and :model_response, and a failed response followed by another attempt carries retry_in_ms. Only the outermost request in a process retries, so an LM that wraps an LM does not multiply attempts. Streamed requests are not sent again. waits must not be empty. Off unless given. A timed-out attempt may have been finished and billed by the provider without a response to record, so a retry can be billed twice; under a deadline each attempt is capped to the time left.
  • Changed: where a call's charge is read. OpenRouter bring-your-own-key billing moved into Imp.Clients.ReqLLM, which records the charge it resolves as :charge in its req_llm response metadata. Imp.Core reads LMResponse.cost from that :charge (final when present, nil included), and otherwise from metadata :cost; it no longer reads usage "cost" or "is_byok". An LM client other than ReqLLM, or a hand-built response envelope, must report its charge as :cost in its metadata (or req_llm.charge), or its cost is nil.
  • Fixed: a forced submit with invalid arguments is extracted. A ReActV2 forced submit whose arguments fail validation now goes to the typed extractor and ends :extracted, where it ended :incomplete with no outputs. If that extraction request fails with an LM error, the call returns {:error, %Imp.Predict.ReActV2.StepError{}}, where it returned {:ok, prediction} ending :incomplete. A forced submit the tool policy refuses still ends :incomplete.

Rollback means restoring 0.15.0 in the lock and removing request_retry:. See the changelog for every change.

Known limits

  • The usage map (:usage on the :model_response event, Imp.Usage, Imp.Prediction.get_lm_usage/1) is ReqLLM's, with input_includes_cached added. Its :cost and :total_cost are ReqLLM's catalog estimate, not a charge, for streamed and non-streamed calls alike, 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.
  • Tool images reach the model as user messages after the turn's tool responses, labelled with the call, not nested in the tool result, even for providers that accept images in tool results. Only MCP text and image blocks are converted; other block types stay text, image URLs in text are never fetched, and the selected model must accept image input of that format and size.
  • ATIF's extra.seen_by_model and the read-as content come from matching a tool message in the next captured request. A result that request does not carry, including one that ended the run, keeps the tool's own output and is marked unseen. agent.tool_definitions comes only from :tools_sent events, and final_metrics totals are left out when any response lacks that figure.
  • A streamed completion that the provider's content filter stops still ends as a completion: the stream's finish_reason is :content_filter and the filter's text has already arrived as chunks. Only non-streamed requests turn it into an Imp.LMError.
  • 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.