Prefer MAX_VBO_CT = N, for valid range 0 to N-1.

really should be MAX_VERTEX_ATTRIB_CT since it's 16 and valid values are 0 to 15

Original names are more accurate! These describe the conversion between VBO values and shader input values. Improved docs would help here, better than renaming.

Yes to these abbreviations.

I'm ok using the more common name of "index buffer".

Gwn_IndexType
Gwn_IndexBuffer
Gwn_IndexBufferBuilder

was copying OpenGL primitive types, but as long as we're abbreviating... how about
GWN_PRIM_LINE_STRIP_ADJ

Using MAX_ as a prefix means not using GWN_ as a prefix. Its also significant that the maximum is associated with Batch and not some other part of the API.

Even with docs, using a generic prefix here will result in a very long name:

NORMALIZE_INT_TO_FLOAT becomes GWN_FETCH_NORMALIZE_INT_TO_FLOAT.

Would GWN_FETCH_I32_TO_F32_NORMALIZE be acceptable?

In that case shouldn't the API be renamed, eg: GWN_elemlist_build -> GWN_indexbuffer_build?

I32 and F32 are too specific. There are cases they don't match.

We could make it

GWN_FETCH_FLOAT
GWN_FETCH_INT
GWN_FETCH_CONVERT
GWN_FETCH_NORMALIZE

GWN_BATCH_MAX_VBO_CT

Gawain uses count and size in most places, length not so much (just for strings).

Drop the _get

GWN_MAX_VERTEX_ATTRIB_CT

Thought about these after you brought them up:

GWN_PrimType_class
GWN_PrimType_belongs_to_class

Done! 620516965b49

Same here, why use FMT instead of FORMAT?

I personally don't see the benefit of shortening for the sake of it. I would use:
GWN_VERT_ATTR_NAME_AVERAGE_LEN, GWN_VERT_ATTR_NAMES_BUFFER_LEN

At least for macros if not also for the function names.

Typo, it should be

GWN_FETCH_FLOAT