We have recently upgraded our runtime to polkadot 0.9.17. We noticed the wasm runtime seems too large i.e. 5.3 MB which exceeds the limit.

Is there a way or best approach to reduce the wasm size?


1 Answer 1


You should use the compressed runtime artefact generated by the build.

For instance in the case of Kusama it is kusama_runtime-v9170.compact.compressed.wasm (note the *.compressed.wasm) as per the assets on the release.

  • Thank you Jaco!
    – Jerry Ren
    Apr 8, 2022 at 5:57
  • I'm guessing the normal runtime.wasm and runtime.compact.wasm are just intemediate build files at this point? (Since compression support is there and there doesn't seem a reason to use them at all anymore)
    – Barto
    Apr 8, 2022 at 6:09
  • 1
    you can use subwasm compress and subwasm decompress to compress and decompress runtimes ( github.com/chevdor/subwasm )
    – Squirrel
    Apr 8, 2022 at 6:15

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