Flash

LoRA post-training for open-weight models: SFT, GRPO, and on-policy distillation. You describe a run in a TOML file, Flash allocates a GPU, trains, streams checkpoints, and serves the resulting adapter.

pip install freesolo-flash
export FREESOLO_API_KEY=fslo_...
flash login
flash train run.toml

The allocator picks the cheapest validated GPU class that fits the run — one dedicated worker allocation per run, on a single GPU today — supervised server-side (stall watchdog, bounded auto-retry resuming from the last streamed checkpoint, endpoint GC).

What this repository is

Flash is the client and control plane for Freesolo's hosted post-training service. This repository contains:

• the flash CLI (flash/cli/) — no declared runtime dependencies (commands that run an environment locally, such as flash env test, need the freesolo SDK),
• the FastAPI control plane (flash/server/) — run submission, auth, project scoping,
• the GPU worker and training recipes (flash/engine/) — verl plus colocated vLLM rollouts,
• the GPU provider substrate (flash/providers/) — pricing, allocation, submit/poll,
• the environment loading machinery (flash/envs/).

The training path is self-hostable end to end: with FLASH_STANDALONE=1, one GPU provider key, and a HuggingFace token, you can run SFT, GRPO, and on-policy distillation on your own hardware budget with no Freesolo backend involved. See SELF_HOSTING.md.

Two components stay Freesolo-operated and are not in this repository:

So there are three honest ways to use Flash: against the hosted service, self-hosted against your own GPU accounts, or as training and provider code to read and modify, which is self-contained and the most reusable part of the repository.

Using the hosted service

Install the client and authenticate with a freesolo API key. flash login is not interactive — pass the key explicitly or export FREESOLO_API_KEY first:

pip install freesolo-flash
export FREESOLO_API_KEY=fslo_...
flash login          # validates the key and stores it in ~/.flash/config.json
flash whoami         # confirm the identity behind it

Every run names an environment, which supplies the task data and the reward or SFT target. Environments are published under a project, which scopes them to an organization:

flash projects create my-project                       # returns a project uuid
flash projects list                                    # look up existing uuids
flash env setup                                        # scaffold environment.py + dataset/train.jsonl
flash env push --project PROJECT_UUID --name my-env .  # returns an environment id

Project ids also appear in your Freesolo dashboard. Every training TOML carries a required top-level project = "<uuid>", which Flash validates against the authenticated organization before it allocates a run. Then describe the run and submit it:

project = "your-project-uuid"
model = "Qwen/Qwen3.5-4B"
algorithm = "sft"

[environment]
id = "your-name/my-env"

[train]
epochs = 1
max_examples = 1000
lora_rank = 32

flash train run.toml                  # submit, prints a run id
flash runs status RUN_ID               # follow it
flash models deploy RUN_ID             # serve the trained adapter
flash models chat RUN_ID -m "hello"    # talk to it

Workload profiles (SFT)

The first flash train or flash train --cost on a new SFT config does not print a quote. It reports that no workload profile exists yet and starts one:

no exact workload profile exists for this config yet, so there is no training quote to
print. the server started a separate profile run that loads your environment and tokenizes
the exact dataset this training would consume.
that profile run is real work and is billed on its own (estimated $0.03); no training run
was created, no training gpu was allocated, and nothing was charged for training.
follow it with `flash runs status profile-sft-...`, then re-run this command once it
reports done.

A profile run loads your environment at its pinned SHA, renders and tokenizes every example this config would train on, and records aggregates: retained and dropped examples, tokens per epoch, supervised tokens, realized max length, packed blocks, and the update horizon. The SFT quote is then computed from those measured tokens rather than from an assumed average example length, and the same profile is what the training worker trains from.

Consequences worth knowing before you submit:

• Profiles are separate runs and separate charges. A profile appears in flash runs list under its own id and is billed for its own (CPU-only, short) work. It is never rolled into the training charge, and a failed profile cannot become training spend.
• Quoting fails closed. If no trustworthy matching profile exists, no training run is created, no GPU is allocated, and no quote is persisted. There is no fallback estimate.
• The cache key is the workload, not the run. Profile ids are derived from environment id, resolved SHA and params; model, revision and tokenizer revision; seed; thinking; worker env; and the [train] fields epochs, batch_size, max_context_tokens, max_steps and max_examples. Change any of them and it is a different workload needing its own profile. Everything else about a run, including which GPU it lands on, is outside the key.
• Profiles are shared across users. The id is a hash of that workload, not of your account, so if someone else already measured your exact config you wait for their profile and are not charged for a second one. Their run is not readable by your key, so the CLI tells you to wait rather than pointing you at a run id that would answer 404.
• A failed profile is retried, not final. If a profile fails or is cancelled, the next submission of that config starts a replacement rather than reporting the workload as permanently unquotable. Because the id is shared, exactly one of the waiting submitters launches the replacement and the rest wait on it.

Run management lives under flash runs (status, log, cancel, checkpoint) and serving under flash models (deploy, chat, deployments, undeploy, export). flash models on its own lists supported base models and flash gpus lists GPU classes with estimated $/hr. To copy a finished adapter into your own HuggingFace repo:

flash models export --adapter-id RUN_ID --repository your-org/your-repo

Intermediate RL checkpoints are deployable too — list them with flash runs checkpoint RUN_ID, then pass RUN_ID/step-N as the adapter id.

There are no built-in task environments — the environment you push defines the task. Single-turn and bounded multi-turn environments are supported.

Calling a deployed adapter from your own app

Deploy once, then POST chat requests with your API key:

export FLASH_API_URL=https://flash.freesolo.co
export FREESOLO_API_KEY=fslo_...
export RUN_ID=flash-1782194170-ce1cfcff

curl -X POST "$FLASH_API_URL/v1/runs/$RUN_ID/deploy" \
  -H "Authorization: Bearer $FREESOLO_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"dry_run": false}'

curl -X POST "$FLASH_API_URL/v1/runs/$RUN_ID/chat" \
  -H "Authorization: Bearer $FREESOLO_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "messages": [{"role": "user", "content": "Write a two-sentence summary of the run."}],
    "temperature": 0.0,
    "max_tokens": 256
  }'

The response uses the OpenAI chat-completions shape; read choices[0].message.content. The run id is the adapter id for serving. If the run is not deployed yet, /v1/runs/<run_id>/chat returns 409 with a hint to deploy first.

Prefer the control-plane endpoint over calling the serving backend directly: it enforces run ownership and forwards per-run serving options such as thinking-mode parity.

Working on the code

The test suite is CPU-only and offline by default. No GPU, no network, no credentials:

uv sync --extra server --dev
uv run pytest -q                         # ~170 test files, offline
uv run ruff check .                      # lint

Those three are exactly what CI runs (.github/workflows/ci.yml).

To exercise the CLI from a dev checkout, invoke the module rather than the flash script:

uv run python -m flash.cli --help

The --dev group installs runpod-flash, which also declares a flash console script, so uv run flash in this environment may launch RunPod's CLI instead of this one. python -m flash.cli is unambiguous. Installed users are unaffected.

Formatting is not enforced repo-wide yet, so run ruff format on the files you touched rather than the whole tree. See CONTRIBUTING.md for the branching model — in short, pull requests go into dev.

Layout

• flash/catalog.py — curated model catalog (Qwen3.5 and Qwen3.6, dense and MoE), VRAM-fit sizing, and each model's thinking capability
• flash/schema/, flash/spec.py — TOML to JobSpec
• flash/runner/ — server-side run supervisor (durable job handle, retries, cost guard, endpoint GC)
• flash/providers/ — GPU substrate (pricing, GPU classes, durable submit/poll, preflight) behind the base.Provider protocol, with allocator.py picking the cheapest fitting class
• flash/engine/ — the on-GPU worker (verl + colocated vLLM rollouts; distillation scores on-policy student samples against a remote teacher) and the shared recipe. SFT targets and RL rewards route through the active environment, so task-specific grading lives with the example, not in the engine
• flash/envs/ — environment registry and the adapter that loads Freesolo SDK environments onto the worker's interface
• flash/serve/, flash/server/ — serving client and the FastAPI control plane (run via the separate flash-server command)
• tests/ — pytest suite (CPU-only, offline-by-default)

Self-hosting

You can run your own control plane against your own GPU accounts, with no Freesolo backend involved. SELF_HOSTING.md is the full guide; the short version:

pip install 'freesolo-flash[server]'   # the base install is client-only

export FLASH_STANDALONE=1
export FREESOLO_INTERNAL_KEY=$(openssl rand -hex 32)
export HF_TOKEN=hf_...
export FLASH_HF_NAMESPACE=your-hf-username   # a namespace your HF_TOKEN can write to
export RUNPOD_API_KEY=...              # or LAMBDA_API_KEY, or VAST_API_KEY

flash-server --host 0.0.0.0 --port 8080

You need one of RunPod, Lambda, or Vast - not all three. Providers whose key is unset are never considered, and the allocator only proposes GPU classes it can actually provision. Startup fails only when all three are missing.

FLASH_STANDALONE=1 is what makes this work: it stops the plane calling out for project, environment, and billing validation, and trusts FREESOLO_INTERNAL_KEY as a single-tenant operator credential. External bearer tokens are rejected rather than accepted unverified. A standalone plane is single-tenant - whoever holds that key can spend your GPU budget, so keep it off untrusted networks. See the security model.

Two seams remain Freesolo-operated and are not part of this repository:

1. Multi-tenant identity. Real per-user keys and org ownership need a backend serving the /api/auth/verify contract in flash/server/auth.py, pointed at by FREESOLO_BASE_URL. Standalone mode is single-tenant instead.
2. Serving. flash/serve/ is a client for a multi-LoRA serving app; point it elsewhere with FREESOLO_SERVING_URL. Training, checkpoint streaming, and adapter export are fully self-hostable - adapters land in your own HuggingFace repos and can be served by any stack that loads LoRA adapters.

The GPU worker image is public and can be pulled directly. It is published under an explicit CUDA tag, not latest:

docker pull ghcr.io/freesolo-co/flash-worker:cu128

Release channels

Two channels are published to PyPI from the same source, distinguished by one line in flash/_channel.py (CHANNEL):

Each environment holds exactly one channel: both packages ship the same import package (flash/) with one baked CHANNEL line, so installing both into the same environment makes the later install win for both CLIs. For side-by-side prod and staging, install each channel in its own virtualenv (or via pipx, which isolates per tool). The dev build is produced by scripts/build_dev_dist.py, which renames the package/CLI and flips CHANNEL to dev before uv build.

Within any single commit the two version fields are locked together: [project].version and [tool.flash-dev].version must match (CI enforces this via .github/workflows/version-parity.yml), so cutting a release means bumping both together. The published channels can still differ, because dev publishes on merge to dev while prod only publishes once dev is promoted to main — so freesolo-flash-dev is normally one or more versions ahead of freesolo-flash.

Either CLI still honours an explicit FLASH_API_URL / the login --api-url flag; the channel only sets the default.

Contributing

See CONTRIBUTING.md. Security issues: SECURITY.md — do not open a public issue.

License

Apache-2.0. See LICENSE and NOTICE.