Imp v0.15.0

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Imp is a framework for typed, optimizable language-model programs on the BEAM. This release adds two ReActV2 options a caller opts into: finish: :tools, which ends a turn only through a finish_on tool, for a program that acts only through its tools, and history_replay: :actions, which shows earlier turns without the text and reasoning written beside their calls. Programs that use neither send byte-for-byte the requests 0.14.1 sent and save as before. New options make this a minor release under Imp's versioning rule.

Install

{:imp, "~> 0.15.0"}

~> 0.15.0 takes later 0.15 patch releases and nothing newer. The two-part form, ~> 0.15, means >= 0.15.0 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 0.14

Change the Imp dependency to {:imp, "~> 0.15.0"}, run mix deps.update imp, and commit mix.lock. No code or data migration is needed: saved programs without the new options load with their defaults.

  • Added: finish: :tools. Only a finish_on tool ends a ReActV2 turn. There is no submit; the outputs come from the finish_on functions. A step that writes text and calls no tool is a thought, followed by one ordinary step and a line naming the ending tools (unsent_note: replaces it). Nothing is forced and no last request is made: a failed request gets one more ordinary step, once per turn and not on the last allowed step; a second thought in a row, a step that says nothing, the step limit or a second failure ends the turn :incomplete, with the request's error in termination_error, or :deadline_exceeded when the deadline has passed. A program with finish: :tools needs a finish_on tool and refuses last_request_note and last_request_tools. A call may give its own finish: (when the task has no input of that name), so a :tools program can ask for one text answer, such as a summary, with finish: :auto.
  • Added: history_replay: :actions. Earlier turns are shown as their inputs, the calls with their results, and their outputs; the text and reasoning written beside the calls, and steps that only wrote text, are left out. The current turn is shown whole: it starts with the call's new inputs or its own last_request_note, or, on a resume with neither, at the last step that carries inputs. The returned history keeps every step. This diverges from DSPy's ReActV2, which replays every step whole; the default, :trajectory, still does. Some thinking APIs reject an earlier tool-call message without its reasoning content; check your provider.
  • Added: unsent_note:. The line shown after each thought-only step, in place of Imp's. A blank line is refused.

Rollback means restoring 0.14.1 in the lock and removing the new options. 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.