Inkling

Inkling is Thinking Machines Lab's open-weight model family built for Tinker: general-purpose models that code, reason, call tools, and accept image and audio input.

Inkling is a Mixture-of-Experts transformer with 975B total parameters and 41B active. Inkling-Small is an efficient sibling at 276B total and 12B active, reaching comparable performance to Inkling at a quarter of its size. Both offer native reasoning over audio and images, variable thinking effort, a context window of up to 1M tokens, and well-rounded performance across a range of benchmarks.

Inkling-Small's efficiency makes it a reasonable default for most tasks, and a natural fit for workloads where cost and latency matter, such as coding, using LLMs to grade, or generating synthetic data for other models. The two share a renderer, tokenizer, and effort interface, so moving between them is a one-line change to the model name, and benchmarking both on your own task is cheap.

Both models are offered as post-trained versions on Tinker, not base models: they arrive instruction-tuned and effort-conditioned, so treat them as starting points for further post-training — SFT, RL, distillation — rather than for continued pretraining.

Working with Inkling differs from other Tinker models in three ways, each covered below: every render needs an explicit thinking-effort value, rendering and tokenization go through tml-renderers rather than a Hugging Face chat template, and the learning rate is yours to calibrate.

Setup

Inkling renders through the standalone tml-renderers package, included in the default installation together with the required torch>=2.10.

Pass thinkingmachines/Inkling or thinkingmachines/Inkling-Small anywhere the cookbook takes a model name. The tokenizer and renderer (tml_v0) are selected automatically for any thinkingmachines/Inkling* model, including the :peft: long-context variants:

from tinker_cookbook import model_info
from tinker_cookbook.renderers import get_renderer
from tinker_cookbook.tokenizer_utils import get_tokenizer

model_name = "thinkingmachines/Inkling"
renderer = get_renderer(model_info.get_recommended_renderer_name(model_name), get_tokenizer(model_name))

Never hardcode a renderer name, and never call tokenizer.encode() to build a prompt — the Inkling tokenizer adapter has no chat template, so raw encoding produces out-of-distribution tokens. The Using Inkling guide is the canonical reference for setup and supported inputs.

Thinking effort: set it everywhere

Inkling's flagship control is continuous thinking effort — a finite scalar in [0.0, 1.0). The renderer turns it into a Thinking effort level system message inserted before the first non-system message. The model is post-trained with that message present, so leaving it to chance means out-of-distribution behavior and unreliable eval numbers.

Rules:

• Set effort explicitly at sampling time and when building training data. The renderer defaults to 0.9 (high) if you omit it, which is a reasonable default but should be a deliberate choice.
• Do not write the effort system message yourself, and do not include a second one in the conversation. The renderer owns it.
• Effort and max_tokens are independent. Higher effort tends to produce longer traces, so raise the generation budget with it or responses truncate mid-thought.

Preset values

These are the same scalars the OpenAI-compatible API uses for its named reasoning_effort presets. Any finite value in [0.0, 1.0) works.

For evaluation: use 0.99 for maximum reasoning performance, 0.0 for benchmarks that do not need chain-of-thought, and sweep the middle for accuracy-versus-latency trade-offs — the thinking-effort guide has effort-scaling results on selected benchmarks. Note that effort=0.0 conditions the model toward no reasoning; it is not a hard constraint.

Think of effort as a general rollout-effort knob, not just a thinking-length knob. Even on tasks that need little reasoning, higher effort can produce more tool calls and more turns, which may help agentic environments.

Sampling

from tinker_cookbook.renderers import Message
from tinker_cookbook.renderers.tml_v0 import TmlV0Renderer
from tinker_cookbook.tokenizer_utils import get_tokenizer

renderer = TmlV0Renderer(get_tokenizer("thinkingmachines/Inkling"))
messages = [Message(role="user", content="Solve this problem step by step.")]
prompt = renderer.build_generation_prompt(messages, effort=0.9)

Sweep effort on your own task before committing to a value, with sample_reasoning.py:

python -m tinker_cookbook.scripts.inkling.sample_reasoning efforts='[0.0,0.2,0.7,0.9,0.99]'

Sample and run evals at temperature=1.0, which is what every script in tinker_cookbook/scripts/inkling/ defaults to. Lowering it is not a substitute for lowering effort.

TmlV0Renderer does not support assistant prefill — pass complete messages and let the model open its own turn. Always pass renderer.get_stop_sequences() in SamplingParams.

Training data

Render supervised data at the same effort you will use at test time, so training tokens match sampling tokens exactly:

model_input, weights = renderer.build_supervised_example(messages_with_response, effort=0.9)

We suggest picking one effort for the whole dataset and using it at test time too, leaning toward the higher end — 0.9 or 0.99 — unless your task genuinely does not need reasoning; mixed-effort training recipes are something we plan to share later. Generic supervised dataset builders currently render at the default 0.9; call build_supervised_example (or build_supervised_examples, which returns multiple examples when a conversation expands to several) directly to render at another effort.

For custom training code built directly on the Tinker SDK and tml-renderers, use render_for_completion_with_effort rather than render_for_completion — the latter omits the effort message.

Post-training

We suggest calibrating the learning rate to your own task and dataset rather than starting from a general-purpose default. hyperparam_utils.get_lr("thinkingmachines/Inkling") deliberately raises NotImplementedError instead of returning a number, so pick a starting value and sweep from there.

• Sweep learning rate and effort together over the first few RL steps. We suggest doing this before committing to any long run, and trying the higher end of your learning-rate range as part of the sweep.
• Watch entropy. The cookbook logs optim/entropy each step. Healthy entropy means the model is still producing variance, which is what makes rewards differ within a group and keeps the model responsive to training.
• Track all-fail and all-success groups. Groups with uniform reward contribute no gradient — see the remove_constant_reward_groups option. If most groups are degenerate, we suggest adjusting task difficulty, group size, or effort.
• Consider an SFT warm-start if RL is slow to move. When your domain or output format sits far from the model's defaults, a short SFT phase on in-format data can reach a regime where RL hill-climbs more readily.

RL defaults are already tuned for Inkling in the cookbook: thinkingmachines/Inkling* models default to the agentic rollout preset and the MinViableGroup rollout strategy (tool-backed rollouts shouldn't discard a whole group over one infrastructure failure). Override with an explicit rollout_config or rollout_error_tolerance if your task is single-turn.

Evaluation

Evaluate through the cookbook sampling path, or through Tinker's OpenAI-compatible or Anthropic-compatible endpoints if your harness expects one of those interfaces. However you sample, set effort explicitly and record it alongside the score — an eval number without its effort value is not reproducible.

The two endpoints expose effort differently. The OpenAI endpoint takes reasoning_effort as either a named preset or a raw float, matching the table above. The Anthropic endpoint takes named levels only, through a Tinker-specific output_config.effort in extra_body — Anthropic's own thinking.budget_tokens is accepted for wire compatibility but ignored — and it does not accept audio input.

Handle parse errors. They occur during training, eval, and normal use, usually when a response is truncated mid-structure. Handle them however fits your pipeline; we suggest retrying recoverable errors with a corrective message that includes the parser error detail.

• Through the cookbook renderer: parse_response() never raises. It returns (message, ParseTermination.MALFORMED) on unparseable output and falls back to decoded raw text. Check the termination value rather than assuming success.
• Through tml-renderers directly: catch tml_renderers.v0.ParseError and feed its string into the corrective message.

If malformed terminations are frequent, check max_tokens first — truncation at an unlucky cut point is the most common cause.

Audio and images

Both models accept audio and image input. Encode media locally through tml-renderers; the renderer accepts raw bytes, a local path, or a base64 data: URI, and deliberately refuses remote URLs. Audio must be WAV, MP3, or FLAC, and non-WAV formats must supply num_frames and sample_rate together. Clean, adequately loud audio noticeably improves results.

python -m tinker_cookbook.scripts.inkling.sample_audio
python -m tinker_cookbook.scripts.inkling.sample_vision

Audio fine-tuning recipes (speech recognition, emotion plus transcription, medical ASR domain adaptation) live in tinker_cookbook/recipes/audio/ and need pip install 'tinker_cookbook[audio]'.

Common pitfalls

Reference

Model and documentation:

• Inkling — model overview and capabilities
• Introducing Inkling — announcement, including controllable thinking effort
• Using Inkling — canonical setup and usage guide
• Thinking effort — presets, sweeps, and effort-scaling results
• Audio and Images — multimodal input requirements
• Models & Pricing — context lengths and pricing per model
• OpenAI-compatible endpoint — reasoning_effort as a named preset or a raw float
• Anthropic-compatible endpoint — point Claude Code or the Anthropic SDKs at a Tinker model; in beta, and no audio input

Packages and code:

• tml-renderers — the rendering library behind tml_v0
• tinker-cookbook — this repository
• sample_reasoning.py — the effort sweep script
• tinker_cookbook/renderers/tml_v0.py — the cookbook renderer adapter
• tinker_cookbook/scripts/inkling/ — runnable sampling scripts for effort, audio, and images
• tinker_cookbook/recipes/audio/ — audio SFT and RL recipes

For general post-training methodology use the research skill; for training or deployment triage use the debug skill.