Split View: RWKV: Reinventing RNNs for the Transformer Era — v4에서 v7 Goose까지

import torch

def wkv_vanilla(w, u, k, v):
    """
    RWKV's WKV mechanism (pure Python implementation)
    w: time decay (negative, larger magnitude = faster decay)
    u: bonus (current token bonus)
    k: key
    v: value
    """
    T, C = k.shape
    output = torch.zeros_like(v)

    for c in range(C):
        # Independent processing per channel (O(T) per channel)
        a = 0.0  # accumulated numerator
        b = 0.0  # accumulated denominator
        p = -1e30  # max value (numerical stability)

        for t in range(T):
            # Current token's contribution
            e1 = torch.exp(torch.clamp(u[c] + k[t, c] - p, max=30))
            e2 = torch.exp(torch.clamp(w[c] + p - p, max=30))  # decay of previous accumulation

            # WKV computation
            wkv = (e1 * v[t, c] + e2 * a) / (e1 + e2 * b)
            output[t, c] = wkv

            # State update (RNN-style)
            new_p = max(w[c] + p, k[t, c])
            e1 = torch.exp(k[t, c] - new_p)
            e2 = torch.exp(w[c] + p - new_p)

            a = e2 * a + e1 * v[t, c]
            b = e2 * b + e1
            p = new_p

    return output

# Training: Transformer mode (parallel)
# Process the entire sequence at once, O(T) complexity
def rwkv_parallel(x, w, u, k_proj, v_proj, r_proj):
    T, C = x.shape
    k = k_proj(x)  # (T, C)
    v = v_proj(x)  # (T, C)
    r = torch.sigmoid(r_proj(x))  # (T, C) reception gate

    # Parallel WKV operation (CUDA kernel)
    wkv = parallel_wkv_cuda(w, u, k, v)

    return r * wkv  # Apply reception gate


# Inference: RNN mode (sequential, constant memory)
def rwkv_sequential(x_t, state, w, u, k_proj, v_proj, r_proj):
    """Process one token at a time, O(1) complexity"""
    k = k_proj(x_t)
    v = v_proj(x_t)
    r = torch.sigmoid(r_proj(x_t))

    # state = (a, b, p) — fixed size!
    a, b, p = state

    e1 = torch.exp(u + k - p)
    e2 = torch.exp(w + p - p)

    wkv = (e1 * v + e2 * a) / (e1 + e2 * b)
    output = r * wkv

    # State update
    new_p = torch.maximum(w + p, k)
    e1 = torch.exp(k - new_p)
    e2 = torch.exp(w + p - new_p)
    new_a = e2 * a + e1 * v
    new_b = e2 * b + e1
    new_state = (new_a, new_b, new_p)

    return output, new_state

class RWKVBlock:
    """
    Basic block structure of RWKV

    Comparison with Transformer Block:
    Transformer: LayerNorm -> Attention -> Add -> LayerNorm -> FFN -> Add
    RWKV:        LayerNorm -> TimeMix   -> Add -> LayerNorm -> ChannelMix -> Add
    """

    def __init__(self, dim, layer_id):
        # Time Mixing (replaces Attention)
        self.time_mix = TimeMixing(dim, layer_id)
        # Channel Mixing (replaces FFN)
        self.channel_mix = ChannelMixing(dim, layer_id)
        self.ln1 = LayerNorm(dim)
        self.ln2 = LayerNorm(dim)

    def forward(self, x, state):
        # Time Mixing (mixes information from past tokens)
        dx, state = self.time_mix(self.ln1(x), state)
        x = x + dx

        # Channel Mixing (mixes information across channels)
        dx = self.channel_mix(self.ln2(x))
        x = x + dx

        return x, state


class TimeMixing:
    """
    Token Shift + WKV
    Linearly interpolates between the current and previous token
    """

    def __init__(self, dim, layer_id):
        self.mix_r = nn.Parameter(torch.ones(dim))  # interpolation ratio
        self.mix_k = nn.Parameter(torch.ones(dim))
        self.mix_v = nn.Parameter(torch.ones(dim))

    def forward(self, x, state):
        # Token Shift: weighted average of current and previous token
        x_prev = state.shift  # previous token
        xr = x * self.mix_r + x_prev * (1 - self.mix_r)
        xk = x * self.mix_k + x_prev * (1 - self.mix_k)
        xv = x * self.mix_v + x_prev * (1 - self.mix_v)

        r = torch.sigmoid(self.W_r(xr))
        k = self.W_k(xk)
        v = self.W_v(xv)

        wkv = compute_wkv(k, v, state)
        return r * wkv, new_state

# RWKV-5: Multi-headed State
# Maintains multiple independent states for improved expressiveness
class RWKV5_TimeMix:
    def __init__(self, dim, n_heads=8):
        self.n_heads = n_heads
        self.head_dim = dim // n_heads
        # Each head has its own independent decay rate
        self.time_decay = nn.Parameter(torch.randn(n_heads, self.head_dim))

# RWKV-6: Data-dependent time decay
# Decay rate changes dynamically based on input (similar to Mamba's selective mechanism)
class RWKV6_TimeMix:
    def forward(self, x, state):
        # Input-dependent decay instead of fixed decay
        time_decay = self.W_decay(x)  # different decay for each input!
        time_decay = torch.exp(-torch.exp(time_decay))

        # LoRA-style decay modulation
        decay_lora = self.decay_lora_a(x)
        decay_lora = torch.tanh(decay_lora) @ self.decay_lora_b
        time_decay = time_decay + decay_lora

# RWKV-7: State Transition Matrix
# Represents state transitions as matrices for richer state updates
class RWKV7_TimeMix:
    """
    Key innovations in RWKV-7:
    1. State Transition Matrix: state transitions via matrices instead of scalars
    2. Enhanced In-Context Learning: dynamically adjusts learning rules
    3. Improved Token Mixing: more sophisticated inter-token information flow
    """

    def forward(self, x, state):
        # Compute state transition matrix
        a = torch.sigmoid(self.W_a(x))  # (B, T, D)
        b = self.W_b(x)                 # (B, T, D)

        # Matrix-form state update
        # s_{t+1} = diag(a_t) @ s_t + k_t^T @ v_t
        k = self.W_k(x)
        v = self.W_v(x)

        # State: (B, H, D/H, D/H) matrix!
        for t in range(T):
            state = torch.diag(a[:, t]) @ state + \
                    k[:, t].unsqueeze(-1) @ v[:, t].unsqueeze(-2)

        return output, state

Performance by model size (Pile dataset perplexity, lower is better):

| Model Size | Transformer | RWKV-4 | RWKV-6 | RWKV-7 |
|-----------|-------------|--------|--------|--------|
| 169M      | 17.2        | 18.1   | 17.4   | 17.0   |
| 430M      | 13.8        | 14.5   | 13.9   | 13.6   |
| 1.5B      | 11.2        | 11.8   | 11.3   | 11.0   |
| 3B        | 9.8         | 10.3   | 9.9    | 9.6    |
| 7B        | 8.5         | 9.0    | 8.6    | 8.3    |
| 14B       | 7.8         | 8.2    | 7.9    | 7.6    |

Inference efficiency (tokens/sec, A100 GPU):

| Sequence Length | Transformer | RWKV-7  |
|----------------|-------------|---------|
| 1K             | 1000        | 1200    |
| 4K             | 800         | 1200    |
| 16K            | 300         | 1200    |
| 64K            | 50          | 1200    |
| 128K+          | OOM         | 1200    |

from transformers import AutoModelForCausalLM, AutoTokenizer

# Load RWKV-7 model
model = AutoModelForCausalLM.from_pretrained(
    "RWKV/rwkv-7-world-3b",
    trust_remote_code=True,
    torch_dtype=torch.bfloat16,
    device_map="auto"
)
tokenizer = AutoTokenizer.from_pretrained(
    "RWKV/rwkv-7-world-3b",
    trust_remote_code=True
)

# Text generation
prompt = "To implement Pod autoscaling in Kubernetes"
inputs = tokenizer(prompt, return_tensors="pt").to("cuda")
outputs = model.generate(
    **inputs,
    max_new_tokens=200,
    temperature=0.7,
    top_p=0.9
)
print(tokenizer.decode(outputs[0], skip_special_tokens=True))

# Install RWKV Runner (GUI tool)
git clone https://github.com/josStorer/RWKV-Runner
cd RWKV-Runner

# Or ChatRWKV (CLI)
pip install rwkv

# Use directly from Python
python3 << 'EOF'
from rwkv.model import RWKV
from rwkv.utils import PIPELINE

model = RWKV(model='/path/to/RWKV-7-World-3B.pth', strategy='cuda fp16')
pipeline = PIPELINE(model, "rwkv_vocab_v20230424")

result = pipeline.generate(
    "Please explain the current state of the AI industry in Korea.",
    token_count=200,
    temperature=0.8
)
print(result)
EOF

| Property            | Transformer    | Mamba          | RWKV-7        |
|---------------------|----------------|----------------|---------------|
| Training Complexity | O(N²)         | O(N)           | O(N)          |
| Inference Complexity| O(N) per token | O(1) per token | O(1) per token|
| Memory              | O(N) KV Cache  | O(1) state     | O(1) state    |
| Parallel Training   | Yes            | Yes (scan)     | Yes (WKV)     |
| Long-range Deps     | Strong         | Good           | Good          |
| In-Context Learning | Strong         | Good           | Enhanced in v7|
| Implementation      | Low            | Medium (CUDA)  | Medium (CUDA) |
| Community           | Massive        | Growing        | Active        |